Thermal and luminescent properties of Eu2+-doped aluminates prepared by the sol-gel method

Alkaline earth aluminates with the overall nominal compositions Ca0.5Sr0.5Al2O4, Ca0.5Mg0.5Al2O4 and Mg0.5Sr0.5Al2O4 doped with 1 mol% of Eu2+ ions were prepared by the modified aqueous sol-gel method. The thermal behaviour of the xerogels was studied by the TG/DSC-MS technique under an argon and a reductive atmosphere (Ar/H-2-5 %). Appropriate luminescent efficiency of the materials was achieved after annealing at temperatures lower than those in conventional solid state reactions. All three aluminates are mixtures of at least two phases; the monoclinic phase of CaAl2O4, the hexagonal phase of SrAl2O4 and the cubic phase of MgAl2O4 were identified. Solid solubility was recognised in the Ca0.5Sr0.5Al2O4:Eu2+ composition due to the similar ionic radii of Ca2+ and Sr2+. UV excited luminescence was observed in the blue region (lambda(max) = 441 nm) in the aluminates containing the monoclinic phase of CaAl2O4 and in the green region (lambda(max) = 520 nm) in the Mg0.5Sr0.5Al2O4:Eu2+ composition.